Projecting Asteroid Impact Corridors onto the Earth

Abstract

Asteroids that collide with the Earth have the potential to deliver widespread destruction to human civilization. The Probabilistic Asteroid Impact Risk (PAIR) software tool is currently being used to model the consequences associated with this natural hazard. Given that initial orbital solutions for a threatening asteroid are subject to uncertainties, the projected impact locations can cover a large area on the Earth's surface, called the impact corridor. The impact corridor not only provides information about the extent and general shape of the exposed area, but also represents a spatial projection of the impact probability distribution on the surface of the Earth. Spatial impact probability information is crucial for asteroid risk assessment, which combines impact consequences and impact probability. While PAIR is currently capable of estimating the impact consequences for a given impact scenario, including a probabilistic representation of the impact corridor will crucially extend its utility in asteroid risk analysis. Here, we present an approach to derive the impact corridor from an initial orbital solution that provides a position and velocity state vector in Cartesian coordinates with a corresponding covariance matrix. Using a Monte Carlo method, a finite set of impact points is generated by sampling the orbital solution state space and propagating the sampled orbits to the ground. The set of impact locations is subsequently used to construct the impact corridor in continuous form on the ground. An analytical or numerical approach may be used to construct the impact corridor from a set of impact points. The analytical approach requires fitting of a probability density function to the impact location set to determine a spatial impact probability distribution. On the other hand, the numerical approach estimates the spatial impact location density at each position in the affected area and scales this information to represent impact probability. The two schemes are compared for their practical applicability within the PAIR tool. The capability to calculate probabilistic impact corridors from orbital data within the PAIR model will enable it to support additional asteroid risk analysis applications, such as risk-informed design for mitigation missions or evaluation of civil response strategies.